1. Technical Field
The present invention relates to a ballast for igniting a high-pressure discharge lamp such as a high-pressure mercury lamp and metal halide lamp, and a projector incorporating the ballast.
2. Related Art
Generally, an igniter circuit has been contained in a ballast, and a high-pressure discharge lamp has been lighted by applying the output of a symmetrical igniter circuit to both electrodes of the high-pressure discharge lamp, or applying the output of an igniter circuit to one electrode of the high-pressure discharge lamp at the time of lighting (see JP-A-2003-316440 and JP-A-2003-151786).
By the way, the structure of the high-pressure discharge lamp causes cooling imbalance between of right and left electrodes at the time of extinction after lighting. When the enclosed mercury liquefies, it adheres more to the electrode at lower temperature (generally, the electrode at the base side) due to the cooling imbalance. Consequently, there has been a problem that, at the next lighting, slow rise in electrode temperature and little progress of mercury vaporization because of undetermined position of glow discharge depending on the output of the normal igniter circuit result in lighting defect. Further, in the lamp for supplying the output of the igniter circuit to one electrode only, there has been a problem that the dielectric strength around the one electrode must be naturally made greater.